1. Field of the Invention
The present invention relates to a toner that is used in recording methods such as electrophotographic methods.
2. Description of the Related Art
Additional improvements in the low-temperature fixability of toners have been required in recent years for electrophotographic machines in order to achieve energy savings. On the other hand, electrophotographic machines are used in a very wide variety of regions, and as a consequence extended exposure to harsher use environments has become a possibility. For example, standing for about 30 days in high temperature, high humidity environments, such as 40° C. and 95% RH, can be foreseen.
Various improvements to the toner resin have been devised in order to improve the low-temperature fixability of toners. For example, styrene-acrylic resins and polyester resins are known as toner resins, but the use of polyester resins is preferred due to their excellent durability and excellent low-temperature fixability.
With regard to such polyester resins, with a view to the low-temperature fixability in particular Japanese Patent No. 3,015,244 proposes a toner that contains a polyester resin that has been at least partially modified by a compound that has a long-chain alkyl group having from 22 to 102 carbon atoms and the hydroxyl group or carboxyl group at a terminal. When this is done, a toner is obtained that exhibits an excellent hot offset resistance and excellent low-temperature fixability in a heat roller-type fixing unit; however, there is room for improvement in on-demand fixing system.
On the other hand, attention has been focused in recent years on crystalline polyester resins, for which the low-temperature fixability and storability can co-exist in good balance. When, in particular, a suitable amount of a crystalline polyester is added to a toner that uses a polyester-type resin as its major component, the polyester-type resin as major component is plasticized and the low-temperature fixability undergoes a substantial improvement.
For example, Japanese Patent Application Laid-open No. 2006-293285 provides a toner having a core/shell structure in the form of a toner that uses a crystalline polyester resin as the core material. This serves to provide a toner for which the low-temperature fixability and storability can co-exist in good balance.
A toner that contains a crystalline polyester resin and a release agent whose endothermic peak temperatures are close to one other is provided by Japanese Patent Application Laid-open No. 2012-234103. According to Japanese Patent Application Laid-open No. 2012-234103, the low-temperature fixability is excellent and control of the gloss value of the image is made possible.
A toner that contains an amorphous polyester resin and a crystalline polyester resin is provided in Japanese Patent No. 4,858,165: this toner uses as the amorphous polyester resin a resin component for which at least one selection from alkylsuccinic acids, alkenylsuccinic acids, and their anhydrides is incorporated and reacted as the acid component.
It is taught here that when this is done, the occurrence of micro non-uniformity in melting during toner melting can be suppressed by the use of an aliphatic crystalline polyester resin as the crystalline polyester resin and the co-use therewith of long-chain alkyl group- and/or alkenyl group-bearing amorphous polyester resins having different molecular weights. Even when variations occur in the amount of heat during fixing, a high-quality color image is then obtained that is free of unevenness in the image gloss value and free of fixing defects, e.g., offset, even in high image density areas.
Thus, as indicated in the preceding, a number of technologies have been introduced by which the low-temperature fixability is improved through the addition of a crystalline polyester.
However, crystalline polyester resins have a slow crystallization rate, and due to this a component that does not completely convert into the crystal is prone to be present in the toner. As a result, when such a toner is allowed to stand for 30 days in a high temperature, high humidity environment, such as 40° C. and 95% RH, the crystalline polyester resin may recrystallize and accompanying this the glass transition temperature (Tg) of the toner may increase, and there is thus a tendency for the low-temperature fixability to be susceptible to a decline in comparison to that prior to standing. This phenomenon is also referred to as the temporal stability below.
The above document, however, is silent on the temporal stability of the state of existence of the crystalline polyester resin during long-term standing in a high temperature, high humidity environment, and room for improvement remains.